The present invention relates generally to the protection of ultrasonic transducers from damage or distruction due to high temperature or the absence of a proper surrounding medium. More particularly, the invention relates to the protection of ultrasonic transducers used in ultrasonic nebulizers.
Ultrasonic nebulizers are utilized in the treatment of a variety of respiratory ailments and conditions. They may be used to humidify the atmosphere of a room, either with water vapor or some prescribed medicament, or they may be used in conjunction with respirator apparatus to provide the same functions. In the operation of a nebulizer, air or some other breathable mixture of gases is pumped through a chamber in the nebulizer in which a fountain of fine droplets of water or other liquid is maintained. A fountain is formed by the action of an ultrasonic transducer, typically a piezoelectric crystal, immersed in the liquid. The liquid to be nebulized is usually placed in a separate vessel separated from, and coupled to, a water chamber by a thin membrane. The transducer is immersed in the water chamber, and the ultrasonic energy is transmitted through the membrane to form the fountain in the medicament vessel.
A recurrent problem with ultrasonic nebulizers of this general type has been damaging ultrasonic transducers by reason of high temperatures, an absence of water surrounding the transducers, or both. Transducer protection has usually taken the form of a temperature detection device coupled to switch off the transducer in the event that some predetermined temperature is reached. Quite often, however, permanent damage can be done to a transducer soon after the surrounding water is gone from the transducer chamber, but before the temperature reaches the predetermined value. Accordingly, there is a definite need for a system of ultrasonic transducer protection which takes into account factors other than the temperature. The present invention fulfills this need.